Radon over Kimberlite Pipes: Surface Field Experiments and Calculations of Vertical Diffusion (Arkhangelsk Diamondiferous Province, NW Russia)

We present the results of field and experimental studies to assess the influence on the formation of the radon field over the kimberlite pipes of the Arkhangelsk diamondiferous province. Measurements were made in the field to establish the radon radiation in the soil air and the gas permeability of soils in the area of the Chidvinskaya pipe. Experimental work was aimed at determining the radiation and physical parameters of the rocks occurring within the kimberlite field. Based on a set of field and experimental data, a model of the diffusion transfer of radon in the area of the Chidvinskaya pipe was calculated for three profiles, represented by the rocks of the pipe, sedimentary rocks of the exocontacts of the pipe, and host sandy and clay sedimentary rocks. The results of the calculations show that the rocks of the exocontacts of the pipe have the greatest potential for increased radon radiation. The calculated values of the radon radiation produced by these rocks exceeded 9000 Bq·m−3. The diatreme kimberlites produced the lowest radon radiation. We showed that the source of the increased values of radon radiation is the rocks of the pipe’s exocontacts. This fact will make it possible to use the emanation method as an additional one for the search for kimberlite pipes.

Migration of 238U and 226Ra Radionuclides in Technogenic Permafrost Taiga Landscapes of Southern Yakutia, Russia

This article describes the features and migration patterns of natural long-lived heavy radionuclides 238U and 226Ra in the major components of the environment including rocks, river waters, soils, and vegetation of permafrost taiga landscapes of Southern Yakutia, which helped us to understand the scale and levels of their radioactive contamination. Different methods have been used in this study to determine the content of 238U and 226Ra in various samples, including gamma-ray spectrometry, X-ray spectroscopy, laser excited luminescence, and emanation method. It was determined that the main source of radioactive pollution of soil and vegetation cover, as well as surface waters in these technogenic landscapes, are the dumps of radioactive rock that were formed here as the result of geological exploration carried out in this area during the last third of the 20th century. The rocks studied were initially characterized by a coarse, mainly stony gravelly composition and contrasting radiation parameters, where the gamma radiation exposure rate varied between 1.71 and 16.7 µSv/h, and the contents of 238U and 226Ra were within the range 126–1620 mg/kg and 428–5508 × 10−7 mg/kg, respectively, and the 226Ra: 238U ratio was 1.0. This ratio shifted later on from the equilibrium state towards the excess of either 238U or 226Ra, due to the processes of air, water, and biogenic migration. Two types of 238U and 226Ra radionuclides migration were observed in studied soils, namely aerotechnogenic and hydrotechnogenic, each of which results in a different intraprofile radionuclide distribution and different levels of radioactive contamination. In this study, we also identified plants capable of selective accumulation of certain radionuclides, including Siberian mountain ash (Sorbus sibiricus), which selectively absorbs 226Ra, and terrestrial green and aquatic mosses, which accumulate significant amounts of 238U.